Vehicle owners must carry at least the minimum required limits of coverage in order to drive in Maryland, legally. Because your policy was canceled, you are subject to uninsured driver penalties, which are assessed at a rate of $150 for the first 30 days then $7 per day afterward. These penalties can add up to $2,500 per year, per vehicle!

(new graphic with uninsured fines @ 3/6/12 mos)
While these penalties are outstanding, you will have a flag against your registration with the MDOT MVA.
In order to reinstate your registration, you will need to resolve these penalties and obtain insurance.
In addition to these penalties, if you have an accident while driving without insurance, you may be personally responsible for any damages.
If you are due to receive a refund from your Maryland tax return, all or part of your refund may also be intercepted as part of the state’s Tax Refund Intercept Program (TRIP).